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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

SÃntese e caracterizaÃÃo de hidrogÃis compÃsitos superabsorventes a base de poliacrilamida e vermiculita. / Synthesis and characterization of composite superabsorbent hydrogels based on polyacrylamide gels and vermiculite.

Ana Paula Dantas de Lima 10 July 2008 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Hydrogels composites of polyacry lamide and hydrogels based on polyacry lamide and vermiculite (PAM/VMT) were synthesized through polymerization reaction i n solution. Organophilic clay was obtained from the cationic exchange reaction with a quaternary ammonium salt. From the modified clay, PAM/VMT was also synthesized. A series of hydrogels were obtained by varying the percentage of clay in relation to the m onomer (5, 10, 20 and 30%) and the crosslinking content added (0.05, 0.1 and 0.2 mol %) to the reaction medium. The hydrogels were characterized by spectroscopy in the infrared region (FTIR), thermogravimetric analysis (TGA), elemental analysis, dynamic rh eology, X - rays and scanning electron microscopy (SEM), absorbance measurements in water, salty environment and variations of pH. The X - rays diffractogram belonging to the organophilic clay demonstrated a displacement of the basal spacing in relation to the non modified clay. In addition to this, typical Infrared bands of the alkyl radical were found. The polyacry lamide and polyac ry lamide/vermiculite hydrogels presented low water ab sorbance capacity values (30 - 35 g H 2 O/g gel). A Fick behaviour was observed fo r the dynamic sorption of hydrogels. Hydrogels with superabsorbent characteristics (Weq > 1000 H 2 O/g gel) were obtained after hydrolysis with NaOH. The capacity of absorbance of water by the hydrogels was increased with the decrease on the concentration of crosslinker and higher W eq values, (swelling in the equilibrium) were observed. The hydrogels showed to be sensitive to the pH variation and to the presence of salts. The hydrogels, even though submitted through a cycle of drying and swelling, conserved t heir superabsorbent characteristics. The rheological behaviour observed is a characteristic of strong gels. The PAM gel with 10% of clay presented higher Gâ a nd Gâ values. The synthesized hydrogels demonstrated better water absorbance properties when c ompa red with commercial polyacry lamide gel. / HidrogÃis compÃsitos de poliacrilamida e a base de poliacrilamida e vermiculita foram (PAM/VMT) sintetizados a partir da reaÃÃo de polimerizaÃÃo em soluÃÃo. Argila organofÃlica foi obtida pela reaÃÃo de troca catiÃnica com um sal quaternÃrio de amÃnio. HidrogÃis a partir dessa argila modificada tambÃm foram sintetizados (PAM/OVMT). Obteve-se uma sÃrie de hidrogÃis variando-se a percentagem de argila em relaÃÃo ao monÃmero (5, 10, 20 e 30%) e a quantidade de reticulante adicionado (0,05; 0,1 e 0,2mol %) ao meio reacional. Os hidrogÃis foram caracterizados por espectroscopia na regiÃo do Infravermelho (FTIR), AnÃlise TermogravimÃtrica (TG), AnÃlise elementar, Reologia dinÃmica, Raios-x e Microscopia eletrÃnica de varredura (MEV), medidas de absorÃÃo em Ãgua, em meio salino e a variaÃÃes de pH. O difratograma de raios-x da argila organofÃlica apresentou um deslocamento do espaÃamento basal com relaÃÃo à argila nÃo modificada. AlÃm disso, apresentou bandas de IV tÃpica dos radicais alquila. Os hidrogÃis de poliacrilamida e poliacrilamida/vermiculita apresentaram baixo valor de capacidade de absorÃÃo de Ãgua (30-35g H2O/g gel). Um comportamento Fickano foi observado para a dinÃmica de sorÃÃo dos hidrogÃis. HidrogÃis com caracterÃsticas superabsorventes (Weq > 1000 H2O/g gel) foram obtidos apÃs a hidrÃlise com NaOH. A capacidade de absorÃÃo de Ãgua pelos hidrogÃis foi aumentada com a diminuiÃÃo da concentraÃÃo de reticulante e maiores valores de Weq (intumescimento no equilÃbrio) foram observados. Os hidrogÃis se mostraram sensÃveis a variaÃÃes de pH e a presenÃa de sais. Os hidrogÃis mesmo submetidos a ciclos de secagem e intumescimento os hidrogÃis conservaram suas caracterÃsticas superabsorventes. O comportamento reolÃgico observado à caracterÃstico de gÃis fortes. O gel de PAM com 10% de argila apresentou maiores valores de Gâ e Gâ. Os hidrogÃis sintetizados mostraram melhores propriedades de absorÃÃo de Ãgua quando comparados com um gel de poliacrilamida comercial.

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